In contrast to impellers of pumps with a shaft, impellers of spherical pumps which form a unit with the rotor of the spherical motor have two tasks; the conveyence of the liquid and the compensation of the weight of the rotor, which is always many times higher than that of a normal impeller. These impellers are therefore diecast from metal. Diecast parts require machining to obtain the final configuration and smoothness of the surface. In addition, any diecast product never has the precision necessary for balance. Therefore, metal impellers have to be balanced on balancing machines. Furthermore, most castable metals are much less resistant than resin materials.